Sensors are used to investigate liquids in different areas. These sensors comprise optical sensors or electrochemical sensors, in order to name only a few examples. The electrochemical sensors work according to an amperometric or potentiostatic measurement principle. Such a sensor is described, for instance, in GB 2 114 304.
Such sensors are placed in a liquid in order to determine certain properties. For example, they determine the cloudiness of the liquid, the oxygen content, the cell growth taking place or similar properties. A bioreactor, in which an above-mentioned sensor is disposed in the liquid used, is described in EP 09006409 and U.S. 61/177,389. In such bioreactors, the sensors are held with the help of pipe connections. These pipe connections are disposed, for example, at the cover of the bioreactor.
The sensors are attached over a press fit or a suitable adapter construction of the type described, for example, in DE 34 04 639. Depending on the fields of application of the liquid, the sensors are directly in contact with the liquid. In accordance with a different form of application, the contact between the sensor and the liquid is avoided, in order to exclude contamination of the liquid by the immersion of the sensor. For this purpose, the sensor is disposed in a tube, which is closed off; such a sensor is also described in EP 09006409 and U.S. 61/177,389. The tubes, used in this example of the application, are closed off by a stopper or a semi-permeable membrane. If the tube is closed off by a semi-permeable membrane, a dissolved oxygen (DO) sensor may be inserted therein for the purpose of determining the oxygen contents of the liquid in a noninvasive manner. For disposing the dissolved oxygen sensor suitably in the bioreactor, the corresponding connection cone is adapted to the cross-section of the dissolved oxygen sensor. Based on this construction, the dissolved oxygen sensor is held in the bioreactor by a frictional connection between the connecting cone and the dissolved oxygen sensor.
At the same time, with the help of the frictional connection, the dissolved oxygen sensor is to be sealed from the outside air. However, it has turned out that the frictional connection between the sensor and the connecting cone seals the interior of the tube only inadequately from the surroundings. An air slot between the sensor and the connecting cone, through which the outside air can penetrate into the tube of the sensor adapter, is already formed when the bioreactor is shaken or vibrated slightly. Additionally, air pressure variations in the environment generate fluctuations of the measured values. Thereby, the measurement of the oxygen concentration in the bioreactor is distorted and destabilized.
As a further disadvantage, it has turned out that, when the dissolved oxygen sensor is introduced into the connecting cone with tube, outside air is pushed in front of the dissolved oxygen sensor in the direction of the membrane.
It is therefore an object of the present invention to make available a sensor adapter, which, in addition to disposing the sensor in a noninvasive manner, also reduces the effects of the surroundings on the measured value determined by the sensor.